1. Field of the Invention
The invention relates to an optical film and a backlight module using the optical film, and particularly to a brightness enhancement film (BEF) and a backlight module using the brightness enhancement film.
2. Description of Related Art
With the progress in display techniques, the flat panel display has become the mainstream among various display devices and replaces the conventional cathode ray tube (CRT). Among the various flat panel displays, the liquid crystal display (LCD) has been deeply favored by the consumers for usage and has been widely used.
FIG. 1 is a schematic diagram of a conventional LCD. As shown in FIG. 1, a liquid crystal display 100 includes a liquid crystal panel 110 and a backlight module 120. The liquid crystal panel 110 may not emit light but determine light transmissive rate, so that a backlight module 120 is disposed behind the liquid crystal panel 110 to be a flat light source of the liquid crystal panel 110. Generally, the backlight module 120 provides a light beam L1, and the light beam L1 propagates to the human eyes through the liquid crystal panel 110 to generate an image. However, when the environmental light L2 (such as sunlight) irradiates the liquid crystal display 100, most of the light is absorbed by the liquid crystal display 100 except for a portion of the light beam L3 reflected by the liquid crystal display 100. In other words, the utilization rate of the environmental light of the conventional liquid crystal display 100 is close to zero.
Moreover, the Taiwan Patent No. 1295355 discloses an optical diffusion module including a plurality of protrusions and a plurality of depressions. The protrusions and the depressions are alternatively arranged in wavy shape. Furthermore, the United States Patent Publication No. 2007/0279727 also discloses a light guide plate having a microstructure with a trapezoid reflection surface, wherein the microstructure is disposed on the lower surface of the light guide plate, and the light beam may be reflected by the light guide plate twice. The United States Patent Publication No. 2007/0279727 further discloses a light guide plate having a microstructure with a triangular reflection surface, wherein the microstructure is disposed on the lower surface of the light guide plate, and the light beam may be reflected by the light guide plate once.
However, by using the aforementioned light guide plate or diffusion film, the environmental light L2 may still not be successfully applied to the display light of the liquid crystal panel 110.